A New View of the Initiation and Propagation in Anionic Polymerization

This work confirms the new view of the initiation and propagation mechanism of the anionic polymerization previously proposed, based on the investigation of anionic bulk‐polymerization of styrene and α‐methyl styrene with the help of a self designed microflow device and characterized by GPC and in situ ⁷Li NMR. It was found that n‐BuLi tended to form the hexameric‐aggregated structure and even to form the huge aggregated structure based on the former. These aggregations of initiators could directly initiate the anionic polymerization and form the supramolecule aggregations. The supramolecule aggregations inevitably blocked the diffusion of the monomers to the ion‐pairs and resulted in a stationary‐conversion platform. Then the aggregators were dissociated completely into equal binary‐aggregated species, and the polymerization continued again rapidly before the termination. Tetrahydrofuran (THF) acted as the electron donator, which could push the electron cloud to Li cation and make the aggregated ring of the active species rather loosened and facilitated the monomer to insert in. Therefore, a little THF can greatly promote the anionic polymerization. However, further addition of THF might block the channel between the ion‐pairs and decrease the propagation rate. It was also found that the aggregated structure of the active species during the anionic polymerization only depends on the initiator aggregations which were formed before the polymerization.     

A New View of the Anionic Diene Polymerization Mechanism

We investigated the anionic polymerization of butadiene in d-heptane solvent using tert-butyl lithium as initiator. Two complementary techniques were used to follow the polymerization processes: ¹H NMR and small angle neutron scattering (SANS). The time resolved ¹H NMR measurements allowed us to evaluate quantitatively the kinetics of the processes involved. The initiation event commences slowly and then progressively accelerates. This indicates an autocatalytic mechanism. The microstructure of the first monomer units attached is to a high extent 1,2. The disappearance of initiator --- at about 10% monomer conversion --- signals the onset of the normal ∼6% vinyl content of the chain. Small angle neutron scattering was used to study the aggregation behavior of the carbon lithium head groups. It is well known that the polar head groups aggregate and form micellar structures. For dienes in non-polar solvents the textbook mechanism assumes the formation of only tetramers during the propagation reaction. By combining ¹H NMR and SANS results we were able to determine quantitatively the aggregation number during all stages of the polymerization. Our measurements show the existence of large-scale structures during the initiation period. The initial degree of aggregation of more than 100 living polymer chains diminished as the polymerization progressed. In addition, even larger, giant structures with N_agg >>1000 and R_g ≈ 1000Å were found.     

苯乙烯-甲基丙烯酸甲酯的高温阴离子溶液共聚

以正丁基锂(n-BuLi)为引发剂、四氢呋喃(THF)为极性调节剂,采用具有较大空间位阻和特定电荷环境的P配合物作为抑制剂,在80℃下实现了苯乙烯(St)与甲基丙烯酸甲酯(MMA)的阴离子嵌段共聚.采用GPC、FT-IR、1H-NMR等手段对共聚物的结构及分子量进行了分析.结果表明:共聚物中各链节的分子量与设计分子量接...     

Sodium Hydride/Trialkylaluminum Complexes for the Controlled Anionic Polymerization of Styrene at High Temperature

Summary: A new generation of anionic initiators (butyllithium free), based on trialkylaluminum and a readily available alkali metal hydride, has been developed for the control of styrene polymerization at high temperature. Triisobutylaluminum and sodium hydride form heterocomplexes that are efficient for the initiation of styrene polymerization at 100 °C in toluene or in bulk. To be active under such conditions, these systems require the presence of an excess of metal hydride with respect to AlR₃ ([Al]/[Na] < 1). PS chains are specifically initiated by the hydrides coming from NaH, and molar masses are controlled in the range 0.8 < [Al]/[Na] < 1. Fast exchange between dormant 1:1 and active 1:2 complexes (Al:Na), and ligand rearrangements within the 1:2 complex, can explain the observed results.

Initiation of styrene with i‐Bu₃Al/NaH systems.     

Trialkylsilyl-Protected Functional Initiators for Stereospecific Anionic Polymerization of Methacrylates

Anionic polymerizations of methyl methacrylate with trialkylsilyl-protected lithium benzylamides were conducted in the presence of aluminum compounds such as n-Bu₃Al. When the Me₃Si-protected amide was used, the carbonyl attack took place to some extent to form a methacrylamide derivative with slightly lower initiator efficiency (∼0.9). In the case of i-Pr₃Si-protected amide, the carbonyl addition was completely suppressed. The obtained polymers had narrow molecular weight distribution and carried benzylamino end-group, as revealed by NMR analysis, which is readily accessible for further chemical transformations such as acylation with acryloyl chloride and debenzylation with H₂/Pd-C. Difuntional initiators with protected groups were also examined.     

New Perspectives in Living/Controlled Anionic Polymerization

Summary: Control of the reactivity and selectivity of active species remains a major challenge in the course of living/controlled polymerizations of vinyl and heterocyclic monomers. We have found that alkyl metal derivatives such as dialkylmagnesium or trialkylaluminum derivatives or the corresponding alkoxyakyl metal derivatives, when added to conventional anionic polymerization systems, are very effective mediators for the controlled anionic polymerization of both styrenic and oxirane monomers. When used as additives to alkali metal alkyl initiators (alkyl lithium, alkyl sodium) for the styrene anionic polymerizations, they strongly retard the reactivity of the propagating species and allow controlling the polymerization in very unusual conditions (bulk, very high temperature). On the contrary, when used in combination to the same alkali metal based initiators for the anionic polymerization of ethylene oxide or propylene oxide, these additives can drastically enhance the reactivity and the selectivity of the propagating species allowing a fast living-like polymerization to proceed already at low temperature in hydrocarbon media.     

Microwave Effects Due to Anionic or Cationic Initiators in Emulsion Polymerization Reactions

Summary: Emulsion polymerization reactions were performed under microwave irradiation and conventional heating using anionic or cationic initiators and surfactants. Microwave irradiation promoted higher reaction rates for both initiators and surfactants, in comparison with the conventional heating. The effect of high power microwave irradiation was studied using a method of cycles of heating and cooling, where rapid polymerization reactions were obtained. In the reactions with anionic initiator and surfactant, a decrease in the particle diameters was observed with microwave heating, and even smaller particles were obtained using high power microwave irradiation. Moreover, the decrease in the particle size was acompanied by an increase in the polymer molecular weight. On the other hand, these effects were not observed for reactions with cationic initiator and surfactant.     

阻滞阴离子聚合的研究进展

介绍了阻滞阴离子聚合引发剂体系近十年的研究现状,详细讨论了几代阻滞引发体系各自的阻滞机理,以及在阴离子聚合制备苯乙烯共聚物树脂中的应用。简单介绍了BASF公司应用阻滞阴离子聚合制备高抗冲聚苯乙烯的应用现状,指出了阻滞阴离子聚合活性可控的优点使其具有更广泛的发展空间。     

Controlling the Polymer Microstructure in Anionic Polymerization by Compartmentalization

An ideal random anionic copolymerization is forced to produce gradient structures by physical separation of two monomers in emulsion compartments. One monomer (M) is preferably soluble in the droplets, while the other one (D) prefers the continuous phase of a DMSO‐in‐cyclohexane emulsion. The living anionic copolymerization of two activated aziridines is thus confined to the DMSO compartments as polymerization occurs selectively in the droplets. Dilution of the continuous phase adjusts the local concentration of monomer D in the droplets and thus the gradient of the resulting copolymer. The copolymerizations in emulsion are monitored by real‐time ¹H NMR kinetics, proving a change of the reactivity ratios of the two monomers upon dilution of the continuous phase from ideal random to adjustable gradients by simple dilution.     

活性阴离子聚合及其单体的研究进展

适用于活性阴离子聚合的单体拓展研究是有关活性阴离子聚合的一项重要的研究工作.本文重点介绍了近十年在活性阴离子聚合领域出现的新型单体的结构设计、合成及其聚合过程的研究进展.文中涉及到的新型单体主要包括非(弱)极性类单体、极性单体及其它单体.进一步细分,非(弱)极性类单体分为苯乙烯衍生物类单体和丁二烯衍生物类单体,极性单体中含有丙烯酸酯类单体、丙烯酰胺类单体、氯乙烯以及N-乙烯基咔唑,其它单体包括异氰酸酯类、烯酮类以及杂环类单体.最后本文对上述这些新型单体中的一些单体用于复杂大分子拓扑结构的设计合成情况也作了简要介绍.     

Controlled Synthesis,Characterization and Application of Novel Functional Fluorinated Polymer By Metal-Free Anionic Polymerization

A well-defined block polymer, di-n-butyl ester terminated poly(2,2,3,4,4,4-hexafluorobutyl methacrylate (BTHFMA), was synthesized by the metal-free anionic polymerization. The tetrabutylammonium salt of di-n-butyl malonate was served as functional carbanionic initiator for the anionic polymerization of 2,2,3,4,4,4-hexafluorobutyl methacrylate in a controlled ‘living’ manner for the first time at ambient temperature. The chemical structure of this product was characterized by FT-IR, ¹H-NMR, and ¹³C-NMR. Gel permeation chromatography (GPC) results showed that the molecular weight of BTHFMA ranged from 1025 to 6582 and the molecular weight distributions were fairly narrow (Mw/Mn = 1.12–1.16). By blending the poly(methyl methacrylate-co-butyl acrylate) [P(MMA-co-BA)] with BTHFMA, we minimized the amount of the BTHFMA used while achieving a hydrophobic surface. The surface properties and compositions of the [P(MMA-co-BA)]/BTHFMA blend films were studied by contact angle and X-ray photoelectron spectroscopy (XPS). The results demonstrated that the 5 wt% blends of BTHFMA could obviously increase hydrophobic ability of the blend with a high water contact angle (98.2^o) and low surface energy (24.2mN/m). XPS results indicated the fluorine mass content of the surface of the 5 wt% blend was up to 26.6%, which suggested BTHFMA enriched on the surface of the blend.     

Structure of Charge Transfer Reaction Complexes Formed in Anionic Polymerization of Isoprene

A new mechanism is suggested for the anionic polymerization of isoprene. The key moment of this mechanism is thermal electron excitation of the complex of a living polymer with a monomer to the low lying S₁ (T₁) state involving a charge (electron) and (Li⁺) cation transfer from the terminal unit to the monomer molecule. It is stated that the probability of chemical bonding depends on the spin density on the radical centers of reactant molecules and on the geometry of the reaction complex. The semiempirical AM1 and ab initio 6-31G* quantum-chemical calculations revealed strong interaction for the ground electronic state of the complex (5-10 kcal/mole) and low energies of the excited triplet levels (<10 kcal/mole).     

Modeling of Anionic Polymerization of Isoprene in an Industrial Reactor

One of the most important reasons for modeling polymerization processes is to provide a tool for estimating the risks of runaway reactions in polymer industry. This is especially important for batch processes, such as anionic polymerization of isoprene or butadiene. This work presents a theoretical and experimental research of the anionic polymerization of isoprene using cyclohexane as solvent and n‐butyllithium as initiator. In the first part, a phenomenological kinetic expression is obtained that describes the anionic polymerization of isoprene initiated by n‐butyllithium in cyclohexane. In the second, the mass and energy balance equations are solved to model the anionic polymerization of isoprene in a quasi‐adiabatic batch reactor. Adjustment of reactor parameters is made using the data obtained from a laboratory reactor. The proposed model predicts adequately the obtained temperature, pressure, and conversion profiles from this set of experiments. Finally, a mathematical model is developed to predict the behavior for the anionic polymerization of isoprene in an industrial reactor.     

Kinetics of the Anionic Polymerization of Buta‐1,3‐diene Considering Different Reactivities of the cis,trans and vinyl Structural Units

The anionic solution polymerization of buta‐1,3‐diene was modeled, considering the reactivity of the active sites to be different due to varying geometric configurations. With the first‐order Markov model, expressions for the fraction of active sites and dyad distribution were obtained. The rate constants were determined by fitting to the conversion and dyad experimental data using the nonlinear least squares method. The kinetic model shows that the microstructure and the dyads do not depend on initiator and butadiene concentration but only on rate constants. Without a modifier, the butadiene addition mechanism is entropic; with a modifier, the mechanism changes to entropic‐enthalpic.

     

Aziridine Termination of Living Anionic Polymerization

A switch from carbanions to aza‐anions is performed by the addition of N‐tosylaziridine (TAz) to living poly(styryl) (PS) chains. This is the first example of carbanionic aziridine ring‐opening which was previously activated by amidation with a tosyl group to enable nucleophilic ring‐opening by the living chain end. Poly(styrene)‐tosylaziridines (PS‐TAz) with narrow molecular weight distributions and variable molecular weights are synthesized. The removal of the tosyl group and subsequent functionalization is shown, evidencing quantitative transfer to azaanionic species. All polymers are characterized in detail by ¹H NMR spectroscopy, DOSY ¹H NMR spectroscopy, and size exclusion chromatography (SEC). This strategy allows the introduction of amine groups via anionic polymerization in analogy to the well‐established epoxide termination.

     

α－甲基丙烯酸2，3－环氧丙基酯的选择性阴离子聚合

通过对α－甲基丙烯酸２，３－环氧丙基酯双键的选择性阴离子聚合的研究发现：在较低温度下（＜－４０℃），聚合中的副反应主要发生在引发阶段，以引发剂与单体中环氧基的副反应为主；当温度较高时（＞－２０℃），则易出现交联现象而难以进行双键的选择性聚合。ＧＰＣ、１ＨＮＭＲ及ＦＴＩＲ鉴定表明，在较低温度下用１，１′二苯基己基锂作引发剂可合成每个重复单元上均定量带有的环氧基的单分散（　＜１．１０）官能性聚合物，该聚合物易溶于多种溶剂。     

Monomer Sequencing in Living Anionic Polymerization Using Kinetic Control

Alternating copolymers containing diphenylethylene (DPE) or diphenylethylene derivatives were prepared by living anionic polymerization using kinetic control. Due to steric hindrance DPE cannot homopolymerize. Therefore alternating copolymers can be prepared by ensuring the rate of cross-propagation (k₁₂) of the co-monomer is favoured over the rate of self-propagation (k₁₁). This reactivity ratio (r₁ = k₁₁/k₁₂) can be controlled by many different factors, such as choice of monomer, electron-donating or withdrawing substituents on DPE, choice of solvent, etc. We report our progress on preparing alternating copolymers by varying these factors.